EP0039652A1 - Preparation of acetic acid by carbonylation - Google Patents

Abstract

Carboxylic acids having the structural formula R1COOH, wherein R1 is a linear, branched or cyclic chain alkyl radical of from 1 to 6 carbon atoms or a phenyl-CnH2n-radical wherein 1</=n</=6, are prepared by carbonylating an alcohol having the formula R1-OH with carbon monoxide in liquid phase, in the presence of a catalytically effective amount of nickel and an alkyl or acyl halide promoter therefor, at a temperature of at least about 120 DEG C. and under a total pressure of less than 200 bars, and said carbonylation being carried out in the presence of at least one vanadium compound in which the vanadium is in an oxidation state of 4 or 5, and in an initial carboxylic acid reaction medium having the formula R2-COOH, wherein R2 is defined as was R1 above, and further wherein R1 and R2 may be the same or different.

Description

The present invention relates to a process for the preparation of carboxylic acids, and more particularly acetic acid, by carbonylation of an alcohol.

It is well known, in particular, that acetic acid can be produced by carbonylation of methanol, under relatively severe pressure conditions, in the presence of nickel and a free or combined halogen.

dans laquelle X représente un atome de brome ou d'iode, M un atome de phosphore ou d'azote, A étant, par exemple, un radical alcoyle inférieur.Thus it has been proposed, in particular, (Cf. Patent of the UNITED STATES OF AMERICA No. 2,729,651) to carry out the carbonylation of methanol in the presence of nickel complexes, obtained by reaction of nickel halides. with quaternary ammonium (or phosphonium) halides, complexes of general formula

in which X represents a bromine or iodine atom, M a phosphorus or nitrogen atom, A being, for example, a lower alkyl radical.

These complexes can be used in this form in the reaction in question, or they can be formed in situ. However, although the pressure used during the carbonylation reaction is high (of the order of 700 atmospheres) the efficiency of the catalytic system, expressed in terms of hourly productivity, is very low.

This productivity, expressed either in relation to the reaction volume, or in relation to the mass of nickel used, has been able to be appreciably improved by involving, on the one hand, a nickel halide and, on the other hand, a quaternary ammonium (or phosphonium) halide in an amount greater than that required by the stoichiometry for the formation of the complexes of formula recalled above. (Cf. German patent 933.148). However, even in the latter case, the pressure conditions remain severe.

More recently, catalytic systems have been proposed making it possible to carbonylate methanol under less severe conditions of pressure. Thus, French patent application 2,370,023 describes the. carbonylation of methanol in the presence of nickel, of a phosphine free and / or complexed with nickel, and of ^l- at least 10 moles of methyl iodide per 100 moles of methanol, under a pressure below 70 bars. However, the efficiency of such a system, expressed in terms of hourly productivity, remains low.

In the context of a low pressure carbonylation process, it has also been pointed out (cf. French patent application 2,404,618) that the presence of solvents, such as carboxylic acids or their esters, has a favorable effect on the progress of the carbonylation reaction. However, the use of such solvents is not essential and the alcohol from which one leaves can serve as solvent.

However, the industrial interest of these recent techniques is compromised by the instability and the cost of the phosphines or amines necessary for their implementation.

It has now been found that it is possible to prepare carboxylic acids, in particular lower alkanoic acids and in particular acetic acid by carbonylation of alcohols in the presence of nickel and at least one halogenated promoter with productivity. remarkable, under relatively mild pressure conditions, while overcoming the aforementioned drawbacks.

The present invention therefore relates to an improved process for carbonylation of alcohols in the liquid phase under a total pressure of less than 200 bars in the presence of an effective amount of nickel, an alkyl or acyl halide, d 'at least one vanadium compound, in which the vanadium is in the oxidation state 4 or -5 and an carboxylic acid initially charged.

It has been unexpectedly found, in particular in the context of the carbonylation of methanol to acetic acid, that the results are not satisfactory if the partial pressure of carbon monoxide is too high; this is all the more surprising since many previous works had highlighted the need to work under very high pressures.

The research which led to the present invention made it possible to bring out the surprising behavior of the compounds of vanadium in which the v.anadium is in the oxidation state 4 or 5, as cocatalysts of the carbonylation reaction of an alcohol, in the liquid phase and. under a total pressure of less than 200 bars. The Applicant has in fact found that the salts and other derivatives of many metals (including carbonyl metals) do not make it possible to react, under the aforementioned conditions, with carbon monoxide on an alcohol, in a carboxylic acid, in the presence of nickel and a halogenated promoter.

dans lequel R représente un radical alkyle linéaire, ramifié ou cyclique renfermant de 1 à 6 atomes de carbone ou un radical -C_nH_2n- dans lequel n est un entier compris entre 1 et 6 (1≤n≤6). Le radical R¹ peut porter un ou plusieurs substituants inertes dans les conditions de réaction de la présente invention. De préférence R¹ représente un radical alkyle inférieur linéaire ou ramifié ayant de 1 à 4 atomes de carbone, et plus particulièrement un radical méthyle.According to the present invention, carbon monoxide is reacted with an alcohol to produce the corresponding carboxylic acid according to the reaction scheme below:

in which R represents a linear, branched or cyclic alkyl radical containing from 1 to 6 carbon atoms or a radical -C _n H _2n - in which n is an integer between 1 and 6 (1 n n) 6). The radical R ¹ can carry one or more substituents which are inert under the reaction conditions of the present invention. Preferably R ¹ represents a linear or branched lower alkyl radical having from 1 to 4 carbon atoms, and more particularly a methyl radical.

The process according to the present invention is carried out in the liquid phase in the presence of a carboxylic acid, of formula R COOH, initially charged, in which R ² has the meaning given for R ¹ , R ² and R ¹ may be identical or different. In other words the carboxylic acid which plays a sort of solvent role is not necessarily the carboxylic acid produced by the carbonylation reaction. However, it may be preferable that the carboxylic acid used as solvent is that produced by the reaction. However, the use of a carboxylic acid heavier than the acid produced as solvent can facilitate the separation operations:

The carboxylic acid R ² COOH represents at least 10% by volume of the initial reaction medium. Preferably, it represents at least 20% by volume of the reaction medium. It can represent a significant part of the reaction environment, in particular in the case of a operation carried out continuously by injecting the alcohol R OH into the carbonylation reactor.

The method according to the invention requires the presence of an effective amount of nickel. Any source of nickel can be used in the context of the present process. Nickel can be introduced in its metallic form (RANEY nickel, for example) or in any other convenient form. As examples of nickel compounds capable of being used for the implementation of the present process, there may be mentioned: carbonate, oxide, hydroxide, halides, in particular iodide, carboxylates, especially acetate, from ni.ckel. Nickel carbonyl is also suitable. RANEY nickel, nickel iodide, nickel acetate and nickel carbonyl are preferably used.

The amount of nickel is not critical. The nickel content which influences the reaction rate is determined as a function of the reaction rate which is considered suitable. Generally, an amount of between 5 and 2000 milligrams of nickel per liter of solution leads to satisfactory results. The operation is preferably carried out with a content of between 20 and 1000 milligrams-grams of nickel per liter.

dans lesquelles X représente un atome de chlore, de brome ou, de préférence, un atome d'iode, et R³ a la signification donnée pour R¹ (et _R ²), _R ³ et R (.ou _R ³ et _R ²) pouvant être identiques ou différents. Bien entendu l'halogénure d'alkyle qui peut être engagé initialement dans le milieu réactionnel, est susceptible d'être formé in situ à partir de dérivés halogénés tels que Cl₂, Br₂, I₂, HC1, HBr, HI, NiBr₂ et NiI₂, et de l'alcool (matière de départ). En d'autres termes une partie ou la totalité de l'halogénure d'alkyle nécessaire à la mise en oeuvre du présent procédé peut être formé à partir de ses "précurseurs" définis ci-avant.The process according to the present invention also requires the presence of at least one alkyl or acyl halide. These halides have the formula R ³ X and

in which X represents a chlorine, bromine atom or, preferably, an iodine atom, and R ³ has the meaning given for R ¹ (and _R ² ), _R ³ and R (.or _R ³ and _R ² ) may be the same or different. Of course, the alkyl halide which can be used initially in the reaction medium, is capable of being formed in situ from halogenated derivatives such as Cl ₂ , Br ₂ , I ₂ , HC1, HBr, HI, NiBr ₂ and NiI ₂ , and alcohol (starting material). In other words, part or all of the alkyl halide necessary for carrying out the present process can be formed from its "precursors" defined above.

It will also be noted that when the halogenated derivative is chosen from nickel compounds, it can be considered as a precursor not only of the alkyl halide but also as a precursor of the metal catalyst. In this particular case, it is preferable to additionally charge, initially, an alkyl or acyl halide and / or a precursor distinct from the nickel halides in question.

In the context of the present invention, lower alkyl iodides having from 1 to 4 carbon atoms constitute a preferred class of alkyl halides. Methyl iodide is particularly suitable for carrying out the process according to the invention.

For a good implementation of the present process a concentration of alkyl or acyl halide of at least 0.5 mol per liter of reaction medium is generally required. Although the increase in the concentration of alkyl or acyl halide has a favorable effect on the reaction rate, it is preferable not to exceed a concentration of the order of 8 moles per liter. As such, a concentration of alkyl or acyl halide of between 0.8 and 6 moles / liter and preferably between 1.5 and 5 moles / liter leads to satisfactory results.

One of the essential characteristics of the present invention resides in the use of at least one vanadium compound, in which the vanadium is at the oxidation state 4 or 5, that is to say at least one compound. chosen from the group consisting of oxides, halides, vanadium (IV) or vanadium (V) oxyhalides and vanadyl bisacetylacetonate. As examples of vanadium compounds suitable for the implementation of the present process, there may be mentioned: VCl ₄ , VOCl ₂ , VOBr ₂ , VO (acac) ₂ , V ₂ O ₅ , VOCl ₃ and VOBr ₃ .

Among the vanadium (IV) compounds, vanadyl bisacetylacetonate [VO (acac) ₂ ] proves to be particularly advantageous in the context of the present invention. Among the vanadium compounds (V), vanadium pentoxide (V ₂ O ₅ ) is preferred. Good results are obtained when the atomic ratio V / Ni is between 0.1 and 100, although lower or higher ratios can be chosen. This ratio is advantageously fixed at a value between 0.2 and 50, and preferably between 0.5 and 25.

A reaction temperature of at least 120 ° C is generally required to obtain a satisfactory reaction rate. A temperature range between 160 and 220 ° C is advantageous.

In the context of the present process, it is not necessary to purify or dry the alcohol and the carboxylic acid initially involved in the reaction. Alcohols and carboxylic acids of technical quality can be used, optionally containing up to 20% by volume of water. On the other hand, all or part of the alcohol R ¹ OH can be used in the reaction in the form of an ester R ² COOR ¹ , R and R ² having the meaning given above, R ¹ and R ² may be identical or different. In this case, it will also initially be necessary to use water in an amount at least equal to the amount theoretically necessary for hydrolyzing the ester initially charged.

The carbonylation process according to the present invention is carried out in the liquid phase under a pressure greater than atmospheric pressure, the pressure however being less than 200 bars. It is more particularly recommended to operate under a partial pressure of - carbon monoxide of between 10 and 100 bars. Carbon monoxide is preferably used in essentially pure form, as it is commercially available. However, the presence of impurities such as, for example carbon dioxide, oxygen, methane and nitrogen is not harmful. The presence of hydrogen is not harmful, even in relatively large proportions.

At the end of the reaction, the reaction mixture is separated into its various constituents by any suitable means, for example by distillation.

The process according to the invention is particularly suitable for the preparation of acetic acid by carbonylation of methanol, in particular in acetic acid. The examples below illustrate the present invention without, however, limiting its field or spirit.

• - AcOH désigne l'acide acétique
• - AcOMe désigne l'acétate de méthyle
• - RR désigne le rapport molaire
  
  c'est-à-dire le rapport molaire entre "l'acide acétique potentiel" formé et (CH₃OH + CH₃I) initial.
• -t désigne la durée effective de l'absorption du monoxyde de carbone à la température de l'essai
• -Pr désigne la productivité, ramenée au temps t (exprimé en heures), en gramme "d'acide acétique potentiel" formé par litre du mélange réactionnel initial

In the examples the following conventions were used:

• - AcOH denotes acetic acid
• - AcOMe denotes methyl acetate
• - RR indicates the molar ratio
  
  that is to say the molar ratio between the "potential acetic acid" formed and (CH ₃ OH + CH ₃ I) initial.
• -t denotes the effective duration of absorption of carbon monoxide at the test temperature
• -Pr denotes the productivity, reduced to time t (expressed in hours), in grams of "potential acetic acid" formed per liter of the initial reaction mixture

EXAMPLE

In a Hastelloy B 2 autoclave, of 125 ml capacity, we load:

After closing the autoclave, the following is established: a pressure of 40 bars of carbon monoxide. The agitation by a back and forth system is started and the autoclave is brought to 200 ° C. in 20 minutes. approximately, using a ring oven. The pressure in the autoclave is then 68 bars; it is then maintained equal to 70 bars by refills of pure CO.

The absorption of carbon monoxide is completed after 75 minutes of reaction at 200 ° C; heating is nevertheless continued for another 45 minutes at this temperature.

After which stirring and heating are stopped; the autoclave is cooled and degassed.

The resulting reaction mixture is analyzed by gas chromatography, after dilution. It contains 44.3 g of acetic acid (RR = 64%). No methyl acetate is detected.

The productivity (Pr) of the acetic acid reaction was therefore 330 grams per hour per liter (g / h x 1).

EXAMPLES 2 to 9

In the apparatus and according to the procedure described above, a series of tests is carried out on a charge comprising methanol, acetic acid, nickel, and unless otherwise indicated, methyl iodide and bisacetylacetonate. vanadyle .. The total duration of the test is 2 hours, unless otherwise stated.

The specific conditions as well as the results obtained appear respectively in Tables I (a) and I (b) below.

The control test (a) also shown in the table is carried out in the absence of vanadium.

The control test (b) also appearing in this table is carried out on a load not containing acetic acid.

Control tests (c) to (n):

In the apparatus and according to the procedure described for Example 1, a series of tests is carried out on a charge comprising 15 ml of methanol, 20 ml of acetic acid and methyl iodide at 180 ° C. and under 70 bars in the presence of various metallic compounds. No reaction was observed after 2 hours at the mentioned temperature.

The specific conditions of these control tests are shown in Table II below.

EXAMPLE 10

In the apparatus and according to the procedure described for Example 1, a test is carried out on a charge comprising 25 ml (232 mMol) of benzyl alcohol, 15 ml of acetic acid, 161 mMol of methyl iodide, 8 mAt-g of nickel - in the form of nickel acetate tetrahydrate and 40 mAt-g of vanadium in the form of vanadyl bisacetylacetonate. The reaction temperature is 180 ° C; the total pressure is maintained at 60 bars, by refilling with pure CO. In 1 hour 30 minutes of reaction at the indicated temperature, 15.8 g of phenylacetic acid are obtained. (RR = 48%).

EXAMPLES 11

Example 1 is repeated above, but adding 40 mMol of potassium iodide to the feed. The absorption of carbon monoxide is terminated after 90 minutes of reaction at 200 ° C; heating is nevertheless continued for 30 minutes at this temperature. The duration total of the test is therefore 2 hours. 45.6 g of acetic acid are then dosed; no methyl acetate is detected. (RR = 69% and Pr = 300 g / hx 1).

Claims (19)

1 - Process for the preparation of a carboxylic acid of formula R ¹ COOH, R ¹ representing a linear, branched or cyclic C ₁ -C ₆ alkyl radical or a -C _n H _2n - radical, 1 = n = 6, by reaction of carbon monoxide on the corresponding alcohol (R ¹ - OH) in the presence of an effective amount of nickel and an alkyl or d.'acyl halide, in the liquid phase. at a temperature greater than or equal to 120 ° C. and under a total pressure less than 200 bars, characterized in that the reaction is carried out in a carboxylic acid of formula R ^{2 -} COOH initially charged, R ² having the meaning given for R ¹ , R ¹ and R ² may be identical or different and, in the presence of at least one compound of. vanadium, in which the vanadium has an oxidation state of 4 or 5. 2.- Method according to claim 1, characterized in that the alkyl or acyl halide is an iodide. 3 - Process according to claim 2, characterized in that the alkyl halide is a C ₁ -C ₄ alkyl iodide- 4 - A method according to claim 3 ,. characterized in that the alkyl iodide is methyl iodide. 5 - Process according to any one of the preceding claims, characterized in that R ¹ is a C ₁ - C ₄ alkyl radical and R ² represents a linear, branched or cyclic C ₁ - C ₆ alkyl radical or an OC radical _n H _2n -, 1 ≤n ≤6. 6 - Process according to claim 5, characterized in that R is a methyl radical. 7 - Method according to any one of the preceding claims ,. characterized in that. the carboxylic acid R ² COOH represents at least 10% by volume of the initial reaction medium. 8 - Method according to any one of the preceding claims, characterized in that the nickel concentration is between 5 and 2000 mAt-g per liter of reaction medium. 9 - Process according to claim 8, characterized in that the nickel concentration is between 20 and 1000 mAt-g per liter of reaction medium. 10 - Process according to any one of the preceding claims, characterized in that the concentration of alkyl or acyl halide is between 0.5 and 8 moles per titer of reaction medium. 11 - Process according to claim 10, characterized in that the concentration of alkyl or acyl halide is between 0.8 and 6 and, preferably, between 1.5 and 5 moles per liter of reaction medium. 12 - Method according to any one of the preceding claims, characterized in that R and R ² are identical. T3 - Process according to any one of the preceding claims, characterized in that the vanadium compounds are chosen from the group consisting of: oxides, halides ,. vanadium (IV) or vanadium (V) oxyhalides and vanadyl bisacetylacetonate. 14 - Process according to claim 13, characterized in that-the vanadium compound is vanadyl bisacetylacetonate. -15 - The method of claim 13 ,. characterized in that. that the vanadium compound is vanadium pentoxide. 16 - Method se.lon any one of claims 13 to 15 ,. characterized in that the atomic ratio V / Ni is between 0.1 and. 100 and preferably between 0.2 and 50. 17 - Process according to claim 16, characterized in that the V / Ni ratio is between 0.5 and 20. 18 - Process according to any one of the preceding claims, characterized in that the reaction temperature is between 160 and 220 ° C. 19 - Method according to any one of the preceding claims, characterized in that the partial pressure of carbon monoxide is between 10 and 100 bars.